The present invention relates to a method of producing a crank arm for a crankshaft of an internal combustion engine, especially for a manually-guided implement such as a power chain saw or the like, wherein the crankshaft is composed of separately produced parts.
DE 34 41 235 C2 discloses a fabricated crankshaft for small internal combustion engines, according to which shaft journals, crank arms and crank bolts are produced separately and are subsequently joined together. Provided in the crank arms are recesses for receiving crankshaft pins and crank bolts. In this connection, a central recess is provided for receiving the shaft journals of the crankshaft on an axis of rotation thereof, and an eccentric recess is provided for receiving the crank bolt at an appropriate spacing relative to the axis of rotation at the level of the central recess. The crank arms of the known arrangement are stamped out of band steel, whereby with the stamped-out contour a flywheel member is defined that is formed on that side of the central recess that is disposed opposite the eccentric recess. In this manner, in conformity with the function of the flywheel member for counterbalancing during crank drive of the internal combustion engine, in the installed state the flywheel member is disposed oppositely from the eccentrically disposed crankshaft pin. The recesses for the crankshaft pin and for the crank bolts are, with the known method, also stamped out of the band steel as is the contour of the crank arm. By means of the stamping process, it is possible in a simple manner, and therefore economically, to stamp out of band steel, in successive stamping processes, a plurality of crank arms. The joined together crankshaft with stamped crank arms enables a multi-purpose and hence economical construction of crank drives for internal combustion engines for driving manually-guided implements such as power chain saws.
The crank arms that are stamped out pursuant to the known method have the same thickness over their entire surface, which corresponds to the thickness of the band steel from which the crank arms were stamped. The arms that are stamped pursuant to the known method are then used for crank arms having simple shapes. However, if counterbalancing is to be improved, the known arms would have to be supplemented by reinforced or thicker wall portions. The thickened wall portions for counterbalancing were attached to the stamped arms as additional components, whereby in the aforementioned DE 34 41 235 C2 sintering was proposed as a joining process for the thicker wall portions.
It is therefore an object of the present invention to improve a method of the aforementioned general type in such a way that stamped crank arms having an improved counterbalancing effect can be produced with simple means.